1. Field of the Invention
This invention relates generally to a method and an apparatus for integrally molding a surface fastener having a large number of engaging elements on both front and back surfaces of a plate-like base portion continuously by extruding a thermoplastic resin and more particularly to a method and an apparatus for efficiently producing a surface fastener having a large number of engaging elements on its both surfaces.
2. Description of the Prior Art
The surface fasteners having engaging elements on both front and back surfaces of base portions are known for example in Japanese Patent Publication No. S 42-8749, Japanese Utility Model Unexamined Publication No. S 55-122612, or Japanese Patent Unexamined Publication No. H 1-238805.
With double-sided surface fastener disclosed in Japanese Patent Publication No. S 42-8749, loops are made of multi-filaments and mono-filaments respectively on front and back surfaces of a cloth by means of a loom and set under heating. Then, mono-filament loops are partially cut to provide hooks, so that loops and hooks are respectively formed on both front and back surfaces of the cloth. The loop elements and hook elements are attached to the resin coated cloth.
The surface fastener having engaging elements on both front and back surfaces disclosed in Japanese Utility Model Unexamined Publication No. S 55-122612 is provided with fibrous hook elements and loop elements on front and back surfaces of a soft tape material. But since the composition of the soft tape material is not apparent, it is not shown that how engaging elements such as hook elements and loop elements are adhered to the soft tape material. However, since the surface fastener disclosed in that Japanese Utility Model Unexamined Publication has engaging elements made of fibers also, it is supposed to be woven by the loom as well as the double-sided surface fastener disclosed in Japanese Patent Publication No. S 42-8749, or to be produced by planting individual fibers on a flexible sheet.
The surface fastener in which a base material and engaging elements are molded of synthetic resin is disclosed in Japanese Patent Unexamined Publication No. H 1-238805. FIG. 18 shows the double-sided surface fastener wherein a plurality of rows of mushroom-shaped engaging elements made of synthetic resin are formed to be protruded on one surface of a base portion, and a plurality of rows of engaging elements having ball-like heads made of the same material are formed to be protruded on the other surface of the base portion. The producing principle of the double-sided surface fastener shall be apparent from the detailed description; A row of engaging elements are molded integrally on the surface of the base portion to provide an elongated narrow tape. Then, sides of plural tapes are adhered and joined by adhesive or adhesive resin with or without a sheet-like joining member of width sufficient as a surface fastener on its back to produce the surface fastener having plural rows of engaging elements of the desired width.
Accordingly, in order to produce the surface fastener disclosed in Japanese Patent Unexamined Publication No. H 1-238805, an elongated narrow tape having a row of a large number of engaging elements protruded therefrom in the longitudinal direction is continuously or discontinuously injection-formed or press-formed. And after the required numbers of tape members are arranged laterally, the sides of the tape members are mutually adhered by the adhesive.
Thus, a textile type surface fastener disclosed in Japanese Patent Publication No. S 42-8749, is characterized in that it is soft to the touch in engagement and disengagement due to peculiar flexibility of textile and flexibility of mono-filament. Since the mono-filament which constitutes the hooks is given a drawing process, the surface fastener has high tensile strength and high bending strength even in small sectional area. Since hooks of high density are formed on account of textile composition, the surface fastener provides high engaging rate and is durable in repetitive use. But since this textile type surface fastener requires much material cost and multi-step process, it is difficult to reduce the manufacturing cost.
In case of producing double-sided surface fastener having fibrous engaging elements on both front and back surfaces of the base portion, it is impossible to impregnate only base portion with resin only by coating or spraying roots of engaging elements with resin in order to adhere and secure the roots to the base portion. It is remarkably difficult to assure the settlement of engaging elements without hardening them. In order to produce the integrally molded surface fastener disclosed in Japanese Patent Unexamined Publication No. H 1-238805, complicated processes are required, causing inefficiency and poor productivity, so that it is impossible to massproduce double-sided surface fastener having a construction shown in FIG. 18 on account of the manufacturing principle. With the surface fastener disclosed in the above-mentioned Publication, since engaging elements are formed to have mushroom-shape or anchor-shape, when the mating engaging elements are composed of loop elements, this surface fastener provides high locking force and smooth engagement without orientation. But it has defects that disengagement of the engaging elements becomes difficult due to the high locking force, and that if engaging elements are forcibly disengaged, the loop elements get broken to have poor durability in repetitive use. In case the mating engaging elements are formed to have the mushroom-shape or anchor-shape, the locking force is remarkably reduced, making the surface fastener useless.